Neurostimulation lead with stiffened proximal array

ABSTRACT

An implantable electrical lead is provided. The electrical lead comprises an electrically insulative, flexible, elongated lead body having a proximal end and a distal end, an electrical contact carried by the distal end of the lead body, an electrical terminal carried by the proximal end of the lead body, an electrical conductor axially extending within the lead body between the electrical contact and the electrical terminal, and a stiffening tube extending within the proximal end of the lead body from a point proximal to the terminal to a point distal to the terminal and proximal to the electrode. An implantable lead assembly kit comprises the implantable electrical lead, and a connector configured for firmly receiving the proximal end of the lead body. A method of implanting the electrical lead comprises introducing the electrical lead into a patient.

FIELD OF THE INVENTION

The present invention relates to tissue stimulation systems, and moreparticularly, to neurostimulation leads.

BACKGROUND OF THE INVENTION

Implantable neurostimulation systems have proven therapeutic in a widevariety of diseases and disorders. Pacemakers and Implantable CardiacDefibrillators (ICDs) have proven highly effective in the treatment of anumber of cardiac conditions (e.g., arrhythmias). Spinal CordStimulation (SCS) systems have long been accepted as a therapeuticmodality for the treatment of chronic pain syndromes, and theapplication of tissue stimulation has begun to expand to additionalapplications such as angina pectoralis and incontinence. Deep BrainStimulation (DBS) has also been applied therapeutically for well over adecade for the treatment of refractory chronic pain syndromes, and DBShas also recently been applied in additional areas such as movementdisorders and epilepsy. Further, in recent investigations PeripheralNerve Stimulation (PNS) systems have demonstrated efficacy in thetreatment of chronic pain syndromes and incontinence, and a number ofadditional applications are currently under investigation. Also,Functional Electrical Stimulation (FES) systems such as the Freehandsystem by NeuroControl (Cleveland, Ohio) have been applied to restoresome functionality to paralyzed extremities in spinal cord injurypatients.

Each of these implantable neurostimulation systems typically includesone or more stimulation leads implanted at the desired stimulation site.In the context of an SCS procedure, one or more stimulation leads areintroduced through the patient's back into the epidural space underfluoroscopy, such that the electrodes carried by the leads are arrangedin a desired pattern and spacing to create an electrode array.

The specific procedure used to implant the stimulation leads in an SCSprocedure will ultimately depend on the type of stimulation leads used.Currently, there are two types of commercially available stimulationleads: a percutaneous lead and a surgical lead.

A percutaneous lead comprises a cylindrical body with ring electrodes,and can be introduced into contact with the affected spinal tissuethrough a Touhy-like needle, which passes through the skin, between thedesired vertebrae, and into the epidural space above the dura layer. Forunilateral pain, a percutaneous lead is placed on the correspondinglateral side of the spinal cord. For bilateral pain, a percutaneous leadis placed down the midline of the spinal cord, or two percutaneous leadsare placed down the respective sides of the midline. In many cases, astylet, such as a metallic wire, is inserted into a lumen runningthrough the center of each of the percutaneous leads to aid in insertionof the lead through the needle and into the epidural space. The styletgives the lead rigidity during positioning, and once the lead ispositioned, the stylet can be removed after which the lead becomesflaccid.

A surgical lead has a paddle on which multiple electrodes are arrangedin independent columns, and is introduced into contact with the affectedspinal tissue using a surgical procedure, and specifically, alaminectomy, which involves removal of the laminar vertebral tissue toallow both access to the dura layer and positioning of the lead.

Each of the above-mentioned implantable neurostimulation systems alsocomprises an implantable neurostimulator, such as an implantable pulsegenerator (IPG), implanted remotely from the stimulation site, butcoupled to the stimulation leads. Thus, electrical pulses can bedelivered from the neurostimulator to the stimulation leads to stimulatethe tissue and provide the desired efficacious therapy to the patient.In the context of an SCS procedure, the electrical pulses are deliveredto the dorsal column and dorsal root fibers within the spinal cord. Thestimulation creates the sensation known as paresthesia, which can becharacterized as an alternative sensation that replaces the pain signalssensed by the patient.

Each stimulation lead may be directly coupled to the neurostimulator orindirectly coupled to the neurostimulator via an extension leads.

If the stimulation leads are to be directly connected to theneurostimulator, the proximal ends of the stimulation leads can beinserted into a connector of the neurostimulator, such that theterminals located at the proximal ends of the stimulation leads arecoupled to corresponding electrical contacts within the connector.Individual wires are routed though lumens in each stimulation lead toconnect the proximally-located terminals with the distally-locatedelectrodes.

If the stimulation leads are to be indirectly connected to theneurostimulator via the extension leads, the proximal ends of thestimulation leads can be inserted into connectors located at the distalends of the respective extension leads, such that the terminals of thestimulation leads are coupled to corresponding electrical contactswithin the connectors of the extension leads. The proximal ends of theextension leads can then be inserted into the connector of theneurostimulator, such that terminals located at the proximal ends of theextension leads are coupled to the corresponding electrical contactswithin the connector of the neurostimulator. Individual wires are routedthough lumens in each extension lead to respectively couple theproximally-located terminals to the distally-located electricalcontacts.

To facilitate introduction of the proximal end of a stimulation lead orextension lead into a corresponding connector, it is desirable that theproximal end be as stiff as reasonably possible to provide the necessarycolumnar strength for the proximal end to overcome the frictional forcesexerted on the lead when inserted into the connector. Simply put, addingstiffness to the proximal end of an electrical lead allows the physicianto easily mate the lead with the connector by grasping the proximal endof the lead and inserting it into the connector without buckling thelead within the physician's hand. At the same time, it is important thatthe remaining portion of the lead be as flexible as reasonably possible,so as to minimize the possibility of tissue trauma/irritation to theepidural and surrounding tissues.

Currently, in the context of SCS procedures, the proximal end of eachelectrical lead is stiffened by backfilling lumens through which theconductors between the electrodes and terminals extends with an epoxy,such as Hysol® epoxy. While Hysol® epoxy provides some stiffnessincrease to the proximal end of the electrical lead, it is limited bythe physical properties of the resin and requires time consumingprocessing steps (precise mixing and heat curing) in manufacturing.

There, thus, remains a need for an alternative method for stiffening theproximal end of an electrical lead, such as a stimulation lead or anextension lead.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present inventions, an implantableelectrical lead is provided. The electrical lead comprises anelectrically insulative, flexible, elongated lead body having a proximalend and a distal end. The electrical lead further comprises anelectrical contact carried by the distal end of the lead body. In oneembodiment, the electrical contact is an electrode. In anotherembodiment, the electrical lead further comprises a connector carried bythe distal end of the lead body, in which case, the electrical contactis contained within the connector. The electrical lead further comprisesan electrical terminal carried by the proximal end of the lead body, andan electrical conductor axially extending within the lead body betweenthe electrical contact and the electrical terminal.

The electrical lead further comprises a stiffening tube extending withinthe proximal end of the lead body from a point proximal to the terminalto a point distal to the terminal and proximal to the electrode. In oneembodiment, the electrical lead comprises a plurality of electricalcontacts carried by the distal end of the lead body, a plurality ofelectrical terminals carried by the proximal end of the lead body, and aplurality of electrical conductors axially extending within the leadbody between the respective electrical contacts and the respectiveelectrical terminals, in which case, the stiffening tube may extend froma point proximal to the plurality of terminals to a point distal to theplurality of terminals and proximal to the plurality of electrodes.

In one embodiment, the stiffening tube and lead body are concentricallydisposed relative to each other. In another embodiment, electrical leadfurther comprises a central lumen extending within the proximal end ofthe lead body, in which case, the stiffening tube may surround thecentral lumen. The stiffening tube may be composed of any relativelystiff material, such as a metallic material. The electrical lead maycomprise a retention sleeve mounted to the proximal end of the lead bodydistal to the electrical contact, in which case, the stiffening tube mayterminate in the lead body at or distal to the retention sleeve. In anoptional embodiment, the electrical lead further comprises a coilextending within the proximal end of the lead body distal to thestiffening tube. The coil may be connected to the stiffening tube.

While the present inventions should not be so limited in their broadestaspects, the stiffening tube provides an effective means for stiffeningthe proximal end of a stimulation lead without having to use a pre-mixedinjected resin filler material. In addition, the coil may provide astrain relief for the stiffening tube, as well as providing somestiffness to the proximal end of the stimulation lead for a physician tograsp.

In accordance with another aspect of the present inventions, animplantable lead assembly kit is provided. The kit comprises thepreviously described implantable electrical lead and a connectorconfigured for firmly receiving the proximal end of the lead body. Inone embodiment, the stiffening tube is configured for being completelydisposed within the connector when the proximal end of the lead body isfully received within the connector. In another embodiment, theelectrical lead further comprises a coil extending within the proximalend of the lead body distal to the stiffening tube, in which case, thecoil may be configured for extending distally from the connector whenthe proximal end of the lead body is fully received within theconnector. In another embodiment, the electrical contact is anelectrode, in which case, the kit may further comprise an extension leadthat carries the connector. In still another embodiment, the kit furthercomprises a neurostimulator that carries the connector.

In accordance with a third aspect of the present inventions, a method ofusing the previously described electrical lead is provided. The methodcomprises introducing the electrical lead into a patient. One method mayfurther comprise inserting the proximal end of the lead body into aconnector having an electrical contact that contacts the electricalterminal. The connector may be carried by a neurostimulator, in whichcase, the method may further comprise providing therapy to the patientby conveying electrical energy from the neurostimulator.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages and objects of the present inventionsare obtained, a more particular description of the present inventionsbriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered limiting of its scope,the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is plan view of one embodiment of a tissue stimulation systemconstructed in accordance with the present inventions;

FIG. 2 is a plan view of the tissue stimulation system of FIG. 1 in usewith a patient;

FIG. 3 is a perspective view of the distal end of a stimulation leadused in the tissue stimulation system of FIG. 1;

FIG. 4 is a perspective view of the proximal end of the stimulation leadused in the tissue stimulation system of FIG. 1;

FIG. 5 is a cross-sectional view of the stimulation lead of FIG. 4,taken along the line 5-5;

FIG. 6 is a cross-sectional view of the stimulation lead of FIG. 4,taken along the line 6-6;

FIG. 7 is a perspective view of a stiffening tube used in the proximalend of the stimulation lead of FIG. 4;

FIG. 8 is a perspective view of the proximal end of a lead body used inthe proximal end of the stimulation of FIG. 4;

FIG. 9 is an axial view of the lead body of FIG. 4, taken along the line9-9;

FIG. 10 is a perspective view of a terminal and associated electricalconductor used in the proximal end of the stimulation lead of FIG. 4;

FIG. 11 is a perspective view of a subassembly of the lead body,electrical contacts, retention sleeve, and electrical conductors used inthe proximal end of the stimulation lead of FIG. 4;

FIG. 12 is an axial view of the subassembly of FIG. 11, taken along theline 12-12;

FIG. 13 is a close-up perspective view of the subassembly of FIG. 11;and

FIG. 14 is a close-up perspective view of the subassembly of FIG. 11,particularly showing the installation of a stiffening tube therein.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The description that follows relates to a spinal cord stimulation (SCS)system. However, it is to be understood that while the invention lendsitself well to applications in SCS, the invention, in its broadestaspects, may not be so limited. Rather, the invention may be used withany type of implantable electrical circuitry used to stimulate tissue.For example, the present invention may be used as part of a pacemaker, adefibrillator, a cochlear stimulator, a retinal stimulator, a stimulatorconfigured to produce coordinated limb movement, a cortical stimulator,a deep brain stimulator, peripheral nerve stimulator, microstimulator,or in any other neural stimulator configured to treat urinaryincontinence, sleep apnea, shoulder sublaxation, headache, etc.

Referring first to FIGS. 1 and 2, a generalized tissue stimulationsystem 10 that may be used in spinal cord stimulation (SCS), as well asother stimulation applications, will be described. The stimulationsystem 10 generally comprises an implantable neurostimulator 12, animplantable stimulation lead 14, which carries an array of electrodes 18(shown exaggerated for illustration purposes), and an implantableextension lead 16. These components can be provided in a kit that canthen be assembled to create the stimulation system 10. Although only onestimulation lead 14 is shown, more than one stimulation lead, andtypically two stimulation leads, can be used in the stimulation system10. As there shown, the proximal end of the stimulation lead 14 isremovably mated to the distal end of the extension lead 16 via aconnector 20 associated with the extension lead 16, and the proximal endof the extension lead 16 is removably mated to the neurostimulator 12via a connector 22 associated with the neurostimulator 12.

In the illustrated embodiment, the neurostimulator 12 takes the form ofan implantable pulse generator (IPG) that comprises an electronicsubassembly 24 (shown in phantom), which includes control and pulsegeneration circuitry (not shown) for delivering electrical stimulationenergy to the electrodes (described below) of the stimulation lead 14 ina controlled manner, and a power supply, e.g., a battery 26 (shown inphantom), so that once programmed and turned on by an externalprogramming device (not shown), the neurostimulator 12 can operateindependently of external hardware.

Alternatively, the neurostimulator 12 can take the form of animplantable receiver-stimulator (not shown), in which case, the powersource, e.g., a battery, for powering the implanted receiver, as well ascontrol circuitry to command the receiver-stimulator, will be containedin an external controller inductively coupled to the receiver-stimulatorvia an electromagnetic link. Alternatively, the neurostimulator 12 cantake the form of an external trial stimulator (ETS)(not shown), whichhas similar pulse generation circuitry as an IPG, but differs in that itis a non-implantable device that is used on a trial basis after thestimulation lead 14 has been implanted and prior to implantation of theIPG, to test the responsiveness of the stimulation that is to beprovided.

The neurostimulator 12 comprises an outer housing 28 for housing theelectronic and other components (described in further detail below), andthe connector 22 to which the proximal end of the stimulation lead 14(or optionally the proximal ends of the extension leads 16) mates in amanner that electrically couples the electrodes 18 to the pulsegeneration circuitry contained within the outer housing 28. The outerhousing 28 is composed of an electrically conductive, biocompatiblematerial, such as titanium, and forms a hermetically sealed compartmentwherein the electronic subassembly 24 and battery 26 are protected fromthe body tissue and fluids. The connector 22 is disposed in a portion ofthe housing 28 that is, at least initially, not sealed.

The connector 22 carries a plurality of contacts (not shown) that comeinto electrical contact with the respective terminals (described infurther detail below) of the stimulation lead 14 or extension lead 16when the proximal end of the stimulation lead 14 or extension lead 16 isinserted into the connector 22. Electrical conductors (not shown), whichextend from the connector 22 in electrical contact with the contacts,penetrate the housing 28 into the sealed chamber and connect to theelectronic subassembly 24. Additional details discussingneurostimulators, including the outer housing 28 and connector 22, aredisclosed in U.S. patent application Ser. No. 11/327,880, entitled“Connector and Methods of Fabrication,” which is expressly incorporatedherein by reference.

As shown in FIG. 2, the stimulation lead 14 is implanted in the epiduralspace 30 of a patient in close proximity to the spinal cord 32. Becauseof the lack of space near the lead exit point 34 where the stimulationlead 14 exits the spinal column, the neurostimulator 12 is generallyimplanted in a surgically-made pocket either in the abdomen or above thebuttocks. The neurostimulator 12 may, of course, also be implanted inother locations of the patient's body. Use of the extension lead 16facilitates locating the neurostimulator 12 away from the lead exitpoint 34. In addition, in some cases, the extension lead 16 may serve asa lead adapter if the proximal end of the stimulation lead 14 is notcompatible with the connector of the neurostimulator 12 (e.g., differentmanufacturers use different connectors at the ends of their stimulationleads and are therefore not compatible with the connector heads of theneurostimulator of another manufacturer). The extension lead 16 may bemade to adapt the stimulation lead 14 to connect the neurostimulator 12to the stimulation lead 14, and hence, “adapt” the stimulation lead 14to the neurostimulator 12. Thus, therapy can be conventionally providedto the patient by conveying electrical energy from the neurostimulator12 to the electrodes 18, which electrical energy is then delivered tothe spinal cord 32 adjacent the electrodes 18.

Referring further to FIGS. 3-5, the stimulation lead 14 comprises anelongated tubular lead body 40 having a proximal end 42 and a distal end44. The lead body 40 may, e.g., have a diameter of between about 0.03inches to 0.07 inches and a length within the range of 30 cm to 90 cmfor spinal cord stimulation applications. The lead body 40 may becomposed of a suitable electrically insulative material, such as, apolymer (e.g., silicone, polyurethane, polytetrafluoroethylene (PTFE),or similar materials), and may be extruded from as a unibodyconstruction.

The stimulation lead 14 further comprises a plurality of electricalcontacts (in this case, the plurality of electrodes 18) mounted to thedistal end 44 of the lead body 40 (FIG. 3), and a plurality ofelectrical terminals 46 mounted to the proximal end 42 of the lead body40 (FIG. 4). In the illustrated embodiment, the stimulation lead 14 is apercutaneous lead, and to this end, the electrodes 18 are arrangedin-line along the lead body 40. In an alternative embodiment, thestimulation lead may take the form of a single paddle lead (not shown),in which case the electrodes 18 may be arranged in a two-dimensionalpattern on one side of a paddle.

Although the stimulation lead 14 is shown as having eight electrodes 18(FIG. 3) and eight corresponding terminals 46 (FIG. 4), the number ofelectrodes and terminals may be any number suitable for the applicationin which the stimulation lead 14 is intended to be use (e.g., two, four,sixteen, etc.). In the illustrated embodiment, each of the electrodes 18and terminals 46 takes the form of a cylindrical ring element composedof an electrically conductive, biocompatible, non-corrosive, material,such as, e.g., platinum, titanium, stainless steel, or alloys thereof.

The stimulation lead 14 further includes a plurality of electricallyinsulative spacers 48 located on the lead body 40 between the respectiveelectrodes 18 and terminals 46. The spacers 48 may be composed of asuitable material, such as, a polymer (e.g., polyurethane or silicone).The stimulation lead 14 further includes a retention sleeve 50 locatedat the proximal end 42 of the lead body 40 just distal to the terminals46. The retention sleeve 50 serves as a hard surface for a mechanicalsecuring element, such as a set screw (not shown), used to secure theproximal end of the stimulation lead 14 within a connector (e.g., eithercarried by the extension lead or the neurostimulator). The stimulationlead 14 further comprises an optional radiopaque marker (not sown)located at the distal tip of the lead body 40.

The stimulation lead 14 also includes a plurality of electricalconductors 54 extending through individual lumens 56 within the leadbody 40 and respectively connected between the electrodes 18 andterminals 46 using suitable means, such as welding, thereby electricallycoupling the distally-located electrodes 18 to the proximally-locatedterminals 46. Each conductor 54 may be composed of a suitableelectrically conductive material, such as platinum, titanium, stainlesssteel, or alloys thereof. In the illustrated embodiment, the conductor54 is a mulifilar cable (1×19 or 1×7) wire made from 28% inner core ofpure silver with 78% outer cladding of MP35N stainless steel. Theconductor 54 is then insulated with a thin outer jacket (0.001″ thick)of Ethylene Tetrafluoroethylene (ETFE) fluoro-based polymer. In theillustrated embodiment, the conductors 54 can be pre-cut and two zoneson the ETFE insulation pre-ablated where they are connected between therespective electrode 18 and terminal 46. The stimulation lead 14 furtherincludes a central lumen 58 that may be used to accept an insertionstylet (not shown) to facilitate lead implantation.

Further details describing the construction of percutaneous stimulationleads are disclosed in U.S. patent application Ser. No. 11/689,918,entitled “Lead Assembly and Method of Making Same,” and U.S. patentapplication Ser. No. 11/565,547, entitled “Cylindrical Multi-ContactElectrode Lead for Neural Stimulation and Method of Making Same,” thedisclosures of which are expressly incorporated herein by reference.Further details regarding the construction of paddle leads are disclosedin U.S. patent application Ser. No. 11/319,291, entitled “StimulatorLeads and Methods for Lead Fabrication,” the disclosure of which isexpressly incorporated herein by reference.

Referring back to FIG. 1, the extension lead 16 is similar to thestimulation lead 14 in that it comprises an elongated lead body 60having a proximal end 62 and a distal end 64, and a plurality ofterminals (not shown) mounted to the proximal end 62 of the lead body60. The lead body 60 of the extension lead 16 may be similarlydimensioned and constructed as the lead body 40 of the stimulation lead14. The extension lead 16 may also include retention sleeve (not shown)much like the retention sleeve 50 of the stimulation lead 14.

The extension lead 16 differs from the stimulation lead 14 in that,instead of electrodes, it comprises the previously mentioned connector20 mounted to the distal end 64 of the lead body 60. The connector 20 isconfigured to accept the proximal end 42 of the stimulation lead 14. Aswill be described in further detail below, the connector 20 carries aplurality of contacts that come into electrical contact with therespective terminals 46 of the stimulation lead 14 when the proximal end42 of the stimulation lead 14 is inserted into the connector 20. In asimilar manner as the stimulation lead 14 (shown in FIGS. 4 and 5), theextension lead 16 also includes a plurality of electrical conductorsextending through individual lumens (both not shown) within the leadbody 60 and connected between the respective terminals and contactsusing suitable means, such as welding, thereby electrically coupling theproximally-located terminals with the distally-located contacts.

Referring now to FIGS. 6-16, specific details regarding the structureand method of manufacturing a stiffened proximal end of the stimulationlead 14 (or alternatively a stiffened proximal end of the extension lead16) will now be described.

Referring initially to FIGS. 6 and 7, the stimulation lead 14 furthercomprises an elongated stiffening tube 66 mounted within the proximalend 42 of the lead body 40. The stiffening tube 66 is composed of amaterial, such as, e.g., stainless steel, that has a higher stiffnessthan does the lead body 40. In the illustrated embodiment, thestiffening tube 66 is in a concentric relationship with the lead body 40and surrounds the central lumen 58. To this end, the inner diameter ofthe stiffening tube 66 may be substantially the same as the diameter ofthe central lumen 58. Alternatively, the stiffening tube 66 may bedisposed within the central lumen 58; that is, the outer diameter of thestiffening tube 66 may be substantially the same as the diameter of thecentral lumen 58. In either event, the stiffening tube 66 extends from apoint that is proximal to the terminals 46 to a point that is justdistal to the terminals 46, thereby stiffening the stimulation lead 14along the terminals 46. The stiffening tube 66 may be retained withinthe lead body 40 using suitable means, such as an interference fit,adhesive bonding, or “reflow” type forming to melt the lead body 40around the stiffening tube 66, thereby locking it to the lead body 40.

As a result, the proximal end 42 of the lead body 40 may be easilyinserted into a connector while minimizing the chance that thestimulation lead 14 will buckle in response to the frictional forceapplied to the lead body 40 by the connector. In the illustratedembodiment, the stiffening tube 66 extends to a point at the retentionsleeve 50, which, as described above, will be frictionally engagedwithin the connector via a set screw. Thus, the stiffening tube 66 willbe completely disposed within the connector when the proximal end 42 ofthe lead body 40 is fully received within the connector (i.e., theelectrical contacts of the connector will have respectively engaged theelectrical terminals 46 of the stimulation lead 14). As a result,maximum flexibility is provided to the stimulation lead 14 outside ofthe connector.

The stimulation lead 14 further comprises a coil 68 mounted within theproximal end 42 of the lead body 40 distal to the stiffening tube 66. Inthe illustrated embodiment, the coil 68 is affixed to stiffening tube66. For example, the coil 68 can be welded to the stiffening tube 66 ormay be machined or fabricated, such as via laser cutting, into thedistal end of the stiffening tube 66. The stiffening tube 66 is formedfrom a helically shaped wire that may be composed of the same materialas the stiffening tube 66. Due to the inherently structural nature of acoil, however, the coil 68 is more flexible than the stiffening tube 66.Like the stiffening tube 66, the coil 68 is in a concentric relationshipwith the lead body 40 and surrounds the central lumen 58. In theillustrated embodiment, the coil 68 has a length of between 0.25-1inches, and thus, assuming that the stiffening tube 66 terminates at theretention sleeve 50, extends from the connector this distance when theproximal end 42 of the lead 14 is fully received within the connector.

Thus, the more flexible coil 68 provides a strain relief where thestiffening tube 66 terminates in the lead body 40. Furthermore, theflexible coil 68, in compression, adds strength to the lead body 40 justdistal to the stiffening tube 66, which can be grasped by the physicianwhen inserting the proximal end 42 of the lead body 40 into theconnector.

Having described the structure of the proximal end of the stimulationlead 14, one method of its manufacture will now be described. Referringto FIGS. 8 and 9, axially disposed channels 70 are formed around theouter circumference of the proximal end 42 of the lead body 40. In theillustrated method, this can be accomplished by ablating the outercircumference of the lead body 40 until a portion of each of the lumens56 is exposed to form the respective channels 70. Next, as illustratedin FIG. 10, each electrical conductor 54 is threaded through a lumen 72of the ring-shaped terminal 46 and attached to the proximal end of therespective terminal 46 using suitable means, such as welding. In theillustrated embodiment, the proximal edge of each terminal 46 includes anotch 74 in which a curved portion 76 of the respective electricalconductor 54 is secured in order to strengthen the connection betweenthe terminal 46 and conductor 54. Alternatively, the electricalconductor 54 may be “blind welded” o the lumen 72 of the respective ofterminal 46.

Next, the retention sleeve 50, and then the terminals 46, along with therespectively attached electrical conductors 54, are threaded over theproximal end 42 of the lead body 40, as illustrated in FIGS. 11-13.While not shown, the spacers 48 (shown in FIG. 4) are also threaded overthe proximal end 42 of the lead body 40 between the respective terminals46. Each terminal 46 is rotationally oriented relative to the lead body40 in a manner that places the respective attached electrical conductor54 into a different channel 70. The electrical conductors 54 are alsodistally introduced from the channels 70 into the lumens 64 extendingthrough the remainder of the lead body 40 and subsequently secured tothe electrodes 18 (shown in FIG. 3) using a suitable means, such aswelding. As best shown in FIG. 13, each channel 70 is deep enough, suchthat the electrical conductor 54 residing in the respective channel 70does not come in contact with the terminals 46 disposed about thechannels 70, but rather only comes into contact with the terminal 46 towhich it is secured. Furthermore, the electrically insulative coating onthe conductors 54 prevents short circuiting with adjacent terminals 46if a conductor 54 happens to come in contact with the inner surface ofthe respective terminal 46.

Next, as shown in FIG. 14, the stiffening tube 66 and associated coil 68are introduced into the central lumen 58 until they are positionedrelative to the terminals 46 and retention sleeve 50 in the mannerdescribed above. As there shown, a proximal portion of the stiffeningtube 66 extends proximally from the lead body 40. Alternatively, thestiffening tube 66 can be completely inserted into the lumen 58. Thespacers 48 (not shown in FIG. 14) are then reflowed (e.g., by exposingthe assembly to a temperature between 140-250 degrees Celsius for aperiod of between 30-120 seconds). The proximal-most tip of the leadbody 40 may be formed using an RF welder, or alternatively, can beformed during the reflow process. In addition, electrically insulativepolyurethane monofilaments or other filler material, such as medicalgrade RTV silicone, can be introduced into the channels 70 and lumens 58prior to reflow to better integrate the resulting assembly and ensureelectrical isolation between the components. Significantly, the use ofthe stiffening tube 66 obviates the need to use rigid filler material,such as Hysol® epoxy, in order to stiffen the proximal end of thestimulation lead 14. Lastly, the terminals 46 and retention sleeve 50are ground down or swaged to provide a uniform outer diameter, and thus,smoother outer surface, to the stimulation lead 14.

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. Thus, the present inventions are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present inventions asdefined by the claims.

What is claimed is:
 1. An implantable electrical lead, comprising: anelectrically insulative, flexible, elongated lead body having a proximalend and a distal end; an electrical contact carried by the distal end ofthe lead body; an electrical terminal carried by the proximal end of thelead body; an electrical conductor axially extending within the leadbody between the electrical contact and the electrical terminal; and astiffening tube extending within the proximal end of the lead body froma point proximal to the electrical terminal to a point distal to theelectrical terminal and proximal to the electrical contact, wherein thestiffening tube and lead body are concentrically disposed relative toeach other.
 2. An implantable lead assembly kit, comprising: theimplantable electrical lead of claim 1; and a connector configured forfirmly receiving the proximal end of the lead body, such that theconnector is electrically coupled to the electrical terminal.
 3. Theimplantable lead assembly kit of claim 2, wherein the stiffening tube isconfigured for being completely disposed within the connector when theproximal end of the lead body is fully received within the connector. 4.The implantable lead assembly kit of claim 2, wherein the implantableelectrical lead further comprises a coil extending within the proximalend of the lead body distal to the stiffening tube, wherein the coil isconfigured for extending distally from the connector when the proximalend of the lead body is fully received within the connector.
 5. Theimplantable lead assembly kit of claim 2, wherein the electrical contactis an electrode, the implantable lead assembly kit further comprising anextension lead that carries the connector.
 6. The implantable leadassembly kit of claim 2, wherein the implantable lead assembly kitfurther comprises a neurostimulator that carries the connector.
 7. Amethod of using the electrical lead of claim 1, comprising introducingthe electrical lead into a patient.
 8. The method of claim 7, furthercomprising inserting the proximal end of the lead body into a connectorhaving an electrical contact that contacts the electrical terminal. 9.The method of claim 8, wherein the connector is carried by aneurostimulator.
 10. The method of claim 9, further comprising providingtherapy to the patient by conveying electrical energy from theneurostimulator.
 11. The implantable electrical lead of claim 1, furthercomprising a coil extending within the proximal end of the lead bodydistal to the stiffening tube.
 12. The implantable electrical lead ofclaim 11, wherein the coil is connected to the stiffening tube.
 13. Theimplantable electrical lead of claim 1, wherein the electrical contactis an electrode.
 14. The implantable electrical lead of claim 1, furthercomprising a connector carried by the distal end of the lead body,wherein the electrical contact is contained within the connector. 15.The implantable electrical lead of claim 1, wherein the stiffening tubeis composed of a metallic material.
 16. The implantable electrical leadof claim 1, further comprising a retention sleeve mounted to theproximal end of the lead body distal to the electrical terminal, whereinthe stiffening tube terminates in the lead body at or distal to theretention sleeve.
 17. The implantable electrical lead of claim 1,further comprising: a plurality of electrical contacts carried by thedistal end of the lead body; a plurality of electrical terminals carriedby the proximal end of the lead body; a plurality of electricalconductors axially extending within the lead body between the respectiveelectrical contacts and the respective electrical terminals; and whereinthe stiffening tube extends from a point proximal to the plurality ofelectrical terminals to a point distal to the plurality of electricalterminals and proximal to the plurality of electrical contacts.
 18. Theimplantable electrical lead of claim 1, wherein the electrical contactand the electrical terminal are mounted directly on the lead body. 19.An implantable electrical lead, comprising: an electrically insulative,flexible, elongated lead body having a proximal end and a distal end; anelectrical contact carried by the distal end of the lead body; anelectrical terminal carried by the proximal end of the lead body; anelectrical conductor axially extending within the lead body between theelectrical contact and the electrical terminal; a stiffening tubeextending within the proximal end of the lead body from a point proximalto the electrical terminal to a point distal to the electrical terminaland proximal to the electrical contact; and a central lumen extendingwithin the proximal end of the lead body, wherein the stiffening tubesurrounds the central lumen.